1. Field of the Invention
The present invention is in the field of substituted 1-arylpyrazole compounds, their synthesis and their use as pest GABA receptor inhibitors and pesticides.
2. Related Art
xcex3-Aminobutyric acid (GABA) receptors are intrinsic membrane glycoproteins in vertebrate and invertebrate neuronal tissues that are members of the ligand-gated ion channel superfamily of receptors. GABA receptors play a major role in the inhibition of central nervous system (CNS) neuronal activity due to the widespread distribution of GABA-releasing and GABA-receptive neurons.
Vertebrate GABA receptors can be divided into two major classes: the GABAA and GABAC subtypes, and GABAB receptor subtype, which are distinguished by differences in their effector mechanisms and pharmacology (Knapp, R. J., et al., Neurochem. Res. 15:105-112 (1990)). GABAA and GABAC receptors are transmitter-operated chloride channels that are activated by GABA to open their chloride channel while GABAB receptors are thought to mediate changes in cyclic AMP levels through the activation of phospholipase activity (Eldefrawi, A. T. and Eldefrawi, M. E., FASEB J. 1:262-271 (1987); Knapp, R. J., et al, Neurochem. Res. 15:105-112 (1990)). The GABAA receptor and its associated chloride ion channel make up the so-called GABAA receptor-channel complex.
GABA is the endogenous ligand for the GABAA receptor of the GABAA-complex, and is the major inhibitory neurotransmitter in the vertebrate brain, in the insect CNS and at insect neuromuscular junctions (Enna et al., In: Benzodiazepine/GABA Receptors and Chloride Channels: Structural and Functional Properties, Alan R. Liss, Inc., New York, pp. 41-56 (1986); Sattelle, D.B., Adv. Insect Physiol. 22:1-113 (1990)). GABA binding to its receptor stimulates chloride ion conductance through the associated chloride ion channel to inhibit synaptic transmission (Knapp, R. J., et al., Neurochem. Res. 15:105-112 (1990); U.S. Pat. No. 5,487,976). When two molecules of GABA bind at sites on the receptor, the chloride channel undergoes a conformational change and opens, allowing chloride ions to flow passively down the electrochemical gradient into the neuron. An influx of chloride into the cell causes a change in the membrane potential, usually a hyperpolarization, which results in an inhibition of the nerve impulse. Blockage of the GABA-gated chloride channel reduces neuronal inhibition, which leads to hyper-excitation of the CNS, resulting in convulsions and death. In contrast, irreversible or hyperactivation of the channel suppresses neuronal activity, resulting in ataxia, paralysis, coma and death (Bloomquist, J. R., Comp. Biochem. Physiol. 106C:301-314 (1993)).
GABAA receptors belong to the class 1 family of neurotransmitter/hormone receptors. Other class 1 members include the glycine receptor, the serotonin type-3 receptor, the nicotinic acetylcholine receptors (muscle and neuronal types) and several excitatory amino acid receptors of vertebrates. Class 1 receptors employ no second messengers and are found where a fast conductance is required. In contrast to class 1 receptors, class 2 receptors (e.g. muscarinic, adrenergic, and others) are coupled to a second messenger and/or a G protein for their transduction, with the channel involved being separate (and usually distant) from the receptor, which is both an agonist-binding and G protein-binding molecule (Barnard, E. A., et al., TiNS 10:502-509 (1987)).
GABAA receptors are pentameric oligomers, of about 250 kilodaltons (kDa), composed of six different types of subunits, xcex1, xcex2, xcex3, xcex4, xcex5 and xcfx81, each of approximately 50 kDa (Olsen, R. W., and Tobin, A. J., FASEB J. 4:1469-1480 (1990); Hevers, W., and Lxc3xcddens, H., Mol. Neurobiol. 18:35-86 (1998)). Each subunit comprises a large extracellular N-terminal domain that putatively includes the ligand-binding site, four hydrophobic presumed membrane-spanning domains, one or more of which contribute to the wall of the ion channel, and a small extracellular C-terminus (Lxc3xcddens, H., and Wisden, W., TiPS 12:49-51 (1991); Olsen, R. W., and Tobin, A. J., FASEB J. 4:1469-1480 (1990); Hevers, W., and Lxc3xcddens, H., Mol. Neurobiol. 18:35-86 (1998)). Heterologous expression in vitro of different combinations of GABA receptor subunit types (xcex1, xcex2, xcex3, xcex4 etc.) and subunit isoforms (xcex11, xcex12, etc. except xcex4) results in heteromultimeric receptors with differing structure and pharmacology (Schofield, P. R., TiPS 10:476-478 (1989); Burt et al., FASEB J. 5:2916-2923 (1991)).
GABA receptors also play an important role in the chemical control of pests, particularly insects, such as fleas, ticks, house flies, fruit flies, plant bugs, boll weevils, grasshoppers, cockroaches, mosquitoes, beetles, locust and moths (Hainzl, D., et al., Chem. Res. Toxicol. 11:1529-1535 (1998)). To date, all insect GABA receptors studied gate a fast acting chloride ion conductance. Although they appear to share many of the properties of GABAA-type receptors in the vertebrate CNS, the majority of receptors in the insect nervous system appear to be bicuculline-, pitrazepin- and RU5135-insensitive (Anthony, N. M., et al., Comp. Mol. Neurobiol., Pichon, Y., ed., Birkhxc3xa4user Verlag, Basel, Switzerland, pp. 172-209 (1993); Wafford, K. A., et al., J. Neurochem. 48:177-180 (1987)). These findings indicate that insect GABA receptors contain several drug binding sites with structural and target site specificities that are different from vertebrate receptor-binding sites (Hainzl, D., et al., Chem. Res. Toxicol. 11:1529-1535 (1998)). Selective insecticides, e.g. insecticides with favorable selective toxicity for insects relative to vertebrates, are based in part on this target-site specificity between the GABA receptors of insects and the GABAA receptors of vertebrates (Moffat, A. S., Science 261:550-551 (1993); Hainzl, D., et al., Chem. Res. Toxicol. 11:1529-1535 (1998)).
Radiolabeled ligand binding studies have considerably expanded our knowledge of insect GABA receptor pharmacology. Within the insect GABA receptor three distinct binding sites have been identified: the GABA receptor agonist binding site, a benzodiazepine binding site and a convulsant binding site (Lummis, S. C. R., Comp. Biochem. Physiol. 95C:1-8 (1990); Rauh, J. J., et al., TiPS 11:325-329 (1990)). The convulsant binding site of GABA receptors in pests is the major target site for many of the drugs and pesticides currently on the market.
Convulsant drugs and pesticides act at the GABA receptor in pest brain, ganglia and muscle as noncompetitive blockers. Inhibition of GABA receptors in pests produces neurotoxicity (e.g. convulsions, paralysis, coma and death). In the early 1980s, the pesticides lindane and cyclodienes (e.g. dieldrin) were shown to antagonize the action of GABA in stimulating chloride uptake by various pest nerve and muscle preparations (Narahashi, T., Phannacol. Toxicol. 78:1-14 (1996)). GABA receptors in pests are also blocked by picrotoxin, phenylpyrazole pesticides (e.g. Fipronil(copyright)), bicyclophosphorous esters (e.g. t-butylbicyclophosphoronthionate), and bicycloorthobenzoates (4-n-propyl-4xe2x80x2-ethynylbicycloorthobenzoate) (U.S. Pat. No. 5,853,002). These pesticides block transmission of signals by GABA, and are very effective on a wide range of economically important pests.
Unfortunately, many potent pesticides and their derivatives also act at the GABAA receptors of animals. For example, fipronil sulfone and desulfinyl fipronil, a metabolite and photoproduct of fipronil, respectively, are not only toxic to pests, but also to upland game birds, freshwater fish and invertebrates, and waterfowl. In addition, fipronil itself is a toxicant for mammals even without oxidation to the sulfone (Hainzl, D., et al., Chem. Res. Toxicol. 11:1529-1535 (1998)).
Pesticides that effectively kill pests but that have little toxicity for animals and humans remain the aim of current research efforts. The present invention addresses the need for the development and use of new and more efficacious pesticides that are highly toxic to pests but not to animals susceptible to pest infestation.
A first aspect of the present invention is directed to a method of inhibiting a pest GABA receptor, comprising contacting a pest GABA receptor with a compound of Formula I.
A second aspect of the invention is directed to a method for controlling pests, comprising contacting an animal, plant or object with a composition comprising a pesticidally effective amount of at least one compound of Formula I, or a salt thereof, and one or more pesticidally-acceptable diluents or carriers.
A third aspect of the invention is pesticidal compositions comprising at least one compound of Formula I, or a salt thereof, and one or more pesticidally-acceptable diluents or carriers.
A fourth aspect of the present invention is directed to novel compounds of Formula I.
A fifth aspect of the present invention is directed to a method for synthesizing compounds of Formula I.
A sixth aspect of the invention is directed to the use of one or more compounds of Formula I for the manufacture of collars or external devices, as well as to a treatment process relating thereto.